This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-036361, filed Feb. 15, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a needle load measuring method, a needle load setting method and a needle load detecting mechanism, particularly, to a method and a mechanism for measuring on the real time basis the needle load applied to a wafer chuck by a probe in the inspecting step and a needle load setting method for setting an appropriate needle load.
A probe apparatus is widely used for inspecting the electrical characteristics of electric circuits formed on a to-be-inspected object, e.g., a wafer. As shown in FIG. 4, the conventional probe apparatus comprises a wafer chuck 1 on which a wafer W is placed, an X-stage 2 for supporting the wafer chuck 1, a Y-stage 3 for supporting the X-stage 2, and a base table 4 for supporting the X-stage 2 and Y-stage 3. When the electrical characteristics of the wafer W are inspected, the wafer chuck 1 is moved in the X- and Y-directions via the X-stage 2 and the Y-stage 3 and is also moved in a vertical direction by a vertical driving mechanism, e.g., member 31 shown in FIG. 1. The X-stage 2 performs a reciprocating movement on the Y-stage 3 along a rail 6 extending in an X-direction via a driving mechanism 5 in the X-direction. On the other hand, the Y-stage 3 performs a reciprocating movement on the base table 4 along a rail 8 extending in a Y-direction via a driving mechanism 7 in the Y direction. The driving mechanism 5 in the X-direction comprises a motor (not shown), and a ball screw 5B. Likewise, the driving mechanism 7 in the Y-direction comprises a motor 7A and a ball screw 7B. The ball screws 5B and 7B are engaged with the X-stage 2 and the Y-stage 3, respectively, so as to move the X- and Y stages 2 and 3. The wafer chuck 1 is moved in the Z direction via the vertical driving mechanism so as to bring the wafer W placed on the wafer chuck 1 into an electrical contact with a plurality of probes 9A of a probe card 9 arranged above the wafer chuck 1. The electrical characteristics of IC chips formed on the wafer W are inspected by the plural probes 9A. During the inspection, the overdriving amount of the wafer chuck 1 is controlled at a predetermined value so as to permit the wafer W to be brought into an electrical contact with the probes 9A.
It is desirable for the overdriving amount to be defined for each probe card 9 in conformity with, for example, the characteristics of the probes 9A. By setting the overdriving amount on the basis of the defined value, the needle load in the inspecting step can be set at a predetermined value. Reference numerals 10A and 10B shown in FIG. 4 denote aligning mechanisms for aligning the position of the wafer W with the position of the probe card 9.
In the conventional inspecting apparatus, the overdriving amount once set is maintained constant until the inspection is finished. A head plate 19B and an adapter ring 19C, to which the probe card is mounted, are considered to be thermally deformed under the influence of, for example, the heat generated from the wafer chuck during the inspection. By the thermal deformation, the magnitude of the needle load is changed over the entire region or a part of the wafer chuck. At the place where the needle load has been diminished, the contact between the wafer and the probes is rendered poor. On the other hand, at the place where the needle load has been increased, the probe card is likely to be damaged.
An object of the present invention is to overcome the above-noted problems inherent in the prior art.
Another object of the present invention is to monitor on the real time basis the contact state (needle load) between a to-be-inspected object, i.e., a wafer, and the probe.
Another object of the present invention is to prevent a damage done to, for example, a probe card.
Further, still another object of the present invention is to provide an improved needle load measuring method, an improved needle load setting method and an improved needle load inspecting mechanism.
According to a first aspect of the present invention, there is provided a method of measuring the needle load applied by a plurality of probes to a wafer chuck in inspecting the electrical characteristics of a to-be-inspected object by using a probe apparatus, comprising the steps of:
overdriving a wafer chuck having a to-be-inspected object mounted thereon by using a wafer chuck lift mechanism so as to bring the to-be-inspected object into contact with a plurality of probes of the probe apparatus; and
measuring the sinking amount of the wafer chuck caused by the needle load applied by the plural probes to the wafer chuck via the to-be-inspected object when the to-be-inspected object is brought into contact with the plural probes;
wherein the needle load corresponding to the measured sinking amount is obtained on the basis of the data showing the relationship between the needle load applied to the wafer chuck and the sinking amount of the wafer chuck caused by the needle load.
According to a second aspect of the present invention, there is provided a method of setting a needle load applied by a plurality of probes to a to-be-inspected object at a predetermined value in inspecting the electrical characteristics of the to-be-inspected object by overdriving a wafer chuck having the to-be-inspected object mounted thereon in a probe apparatus so as to bring the to-be-inspected object into an electrical contact with the plural probes, comprising the step of:
detecting the sinking amount of the wafer chuck caused by the needle load applied by the plural probes in the process of overdriving the wafer chuck;
wherein the needle load applied to the to-be-inspected object mounted on the wafer chuck is set at a predetermined value by setting the sinking amount detected in the step at a sinking amount corresponding to a predetermined needle load on the basis of the data showing the relationship between the needle load applied to the wafer chuck and the sinking amount of the wafer chuck caused by the needle load.
In the method according to each of the first and second aspects of the present invention described above, it is desirable for the sinking amount of the wafer chuck to be measured at a plurality of points of the wafer chuck.
In the method according to each of the first and second aspects of the present invention described above, it is desirable for the wafer chuck having the to-be-inspected object mounted thereon to be overdriven by a lift mechanism comprising a ball screw, a driving mechanism for rotating the ball screw and a nut member.
In the method according to each of the first and second aspects of the present invention described above, it is desirable for the step of measuring the sinking amount to comprise the sub-steps of:
detecting a pseudo overdriving amount of the wafer chuck performed by the lift mechanism, the pseudo overdriving amount being the overdriving amount of the wafer chuck performed by the lift mechanism when the needle load is not applied to the wafer chuck;
detecting the actual overdriving amount of the wafer chuck performed by the lift mechanism, the actual overdriving amount being the actual overdriving amount of the wafer chuck performed by the lift mechanism when the needle load is applied to the wafer chuck; and
obtaining the sinking amount of the wafer chuck from the difference between the pseudo overdriving amount and the actual overdriving amount.
In the method described above, it is desirable for the step of detecting the pseudo overdriving amount to comprise the process of detecting the pseudo overdriving amount on the basis of the amount of rotation of the driving mechanism for rotating the ball screw measured by a rotary encoder.
In the method described above, it is desirable for the step of detecting the actual overdriving amount to comprise the process of detecting the actual overdriving amount of the wafer chuck by a linear encoder.
According to a third aspect of the present invention, there is provided a probe apparatus for inspecting the electrical characteristics of a to-be-inspected object, comprising:
a wafer chuck for mounting a to-be-inspected object thereon;
a lift mechanism for vertically moving the wafer chuck;
a plurality of probes brought into an electrical contact with a plurality of electrodes of the to-be-inspected object mounted on the wafer chuck overdriven by the lift mechanism;
a measuring mechanism for measuring the sinking amount of the wafer chuck caused by the needle load applied by the plural probes to the to-be-inspected object when the wafer chuck is overdriven to bring the to-be-inspected object mounted on the wafer chuck into contact with the plural probes; and
a needle load detecting mechanism for obtaining the needle load corresponding to the measured sinking amount on the basis of the data showing the relationship between the needle load applied to the wafer chuck and the sinking amount of the wafer chuck.
In the measuring mechanism of the probe apparatus described above, it is desirable for the sinking amount of the wafer chuck to be measured at a plurality of points of the wafer chuck.
It is desirable for the lift mechanism of the probe apparatus described above to comprise a ball screw, a driving mechanism for rotating the ball screw and a nut member.
It is desirable for the measuring mechanism of the probe apparatus for measuring the sinking amount to comprise:
a first lift amount detecting mechanism for detecting a pseudo lift amount of the wafer chuck performed by the lift mechanism, the first lift amount detecting mechanism detecting a pseudo overdriving amount that the lift mechanism may overdrive the wafer chuck when the needle load is not applied to the wafer chuck;
a second lift amount detecting mechanism for detecting the actual overdriving amount of the wafer chuck performed by the lift mechanism, the second lift amount detecting mechanism detecting the actual overdriving amount of the wafer chuck performed by the lift mechanism when the needle load is applied to the wafer chuck;
a calculating mechanism for obtaining the sinking amount of the wafer chuck from the difference between the pseudo overdriving amount detected by the first lift amount detecting mechanism and the actual overdriving amount detected by the second lift amount detecting mechanism;
a storing device for storing the data showing the relationship between the needle load applied to the wafer chuck and the sinking amount of the wafer chuck caused by the needle load; and
a needle load detecting mechanism for obtaining the needle load corresponding to the sinking amount of the wafer chuck obtained by the calculating mechanism on the basis of the data showing the relationship between the needle load applied to the wafer chuck and the sinking amount of the wafer chuck caused by the needle load.
In the probe apparatus of the present invention, it is desirable for the measuring mechanism of the sinking amount to comprise:
a first lift amount detecting mechanism for detecting a pseudo lift amount of the wafer chuck performed by the lift mechanism, the first lift amount detecting mechanism detecting a pseudo overdriving amount that the lift mechanism may overdrive the wafer chuck when the needle load is not applied to the wafer chuck;
a second lift amount detecting mechanism for detecting the actual overdriving amount of the wafer chuck performed by the lift mechanism, the second lift amount detecting mechanism detecting the actual overdriving amount of the wafer chuck performed by the lift mechanism when the needle load is applied to the wafer chuck;
a calculating mechanism for obtaining the sinking amount of the wafer chuck from the difference between the pseudo overdriving amount detected by the first lift amount detecting mechanism and the actual overdriving amount detected by the second lift amount detecting mechanism;
a storing device for storing the data showing the relationship between the needle load applied to the wafer chuck and the sinking amount of the wafer chuck caused by the needle load; and
a needle load detecting mechanism for obtaining the needle load corresponding to the sinking amount of the wafer chuck obtained by the calculating mechanism on the basis of the data showing the relationship between the needle load applied to the wafer chuck and the sinking amount of the wafer chuck caused by the needle load.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.